The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A nuclear reactor pressure vessel (RPV) has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide is spaced above a core plate within the RPV. A core shroud, or shroud, surrounds the core plate and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. The top guide includes several openings, and fuel assemblies are inserted through the openings and are supported by the core plate. The core plate includes a flat plate supported by a plurality of beams.
A nuclear reactor core includes a plurality of individual fuel assemblies that have different characteristics that affect the strategy for operation of the core. For example, a nuclear reactor core typically has several hundred individual fuel assemblies that have different characteristics, each fuel bundle having a plurality of fuel rods. The fuel assemblies are arranged within the reactor core so that the interaction between the fuel assemblies satisfies regulatory and reactor design guidelines and constraints. In addition, the core arrangement determines the cycle energy, which is the amount of energy that the reactor core generates before the core needs to be refreshed with new fuel elements. The core loading arrangement preferably optimizes the core cycle energy.
A core cycle is determined from one periodic reactor core refueling to a second reactor core refueling. During the course of the cycle of operation, the excess reactivity, which defines the energy capability of the core, is controlled in two ways. Specifically, a burnable poison, e.g., gadolinia, is incorporated in the fresh fuel. The quantity of initial burnable poison is determined by design constraints typically set by the utility and by the NRC. The burnable poison controls most, but not all, of the excess reactivity. A second way is through the manipulation of control rods within the core. Control rods control the excess reactivity. Specifically, the reactor core contains control rods, which assure safe shutdown and provide the primary mechanism for controlling the maximum power peaking factor. The total number of control rods available varies with core size and geometry, and is typically between 50 and 269 in a reactor core. The position of the control rods, i.e., fully inserted, fully withdrawn, or somewhere between, is based on the need to control the excess reactivity and to meet other operational constraints, such as the maximum core power peaking factor.
Coolant is introduced in the core to cool the core and to be transitioned into steam as a working fluid for energy generation. Normal coolant flow enters the fuel assemblies as a single phased flow with slightly sub-cooled coolant. The flow approaches the fuel support vertically upward and then turns horizontally as the flow enters the inlet to a fuel support supporting a fuel assembly. The flow then passes through an orifice of the fuel support to provide a pressure drop to assist coolant distribution to the fuel assemblies. The flow then turns vertical and enters the lower tie plate of the fuel assembly and is distributed around the individual fuel rods of the fuel assembly.
It is known that reactor core design can be varied by design and layout of the control rods within the fuel assembly lattice. Often, the fuel assembly lattice is configured with differently configured fuel rods such that the fuel assembly has a defined orientation. The core is designed with a plurality of oriented fuel assemblies to improve the performance and operation of the reactor. However, fuel assemblies typically have a round shaped tie plate configured for mating with a round hole or orifice defined by the fuel support. The tie plate's rod shaped end includes a lumen for receiving fluid flow from the fuel support. Current tie plates, fuel assemblies, and fuel supports do not provide any capabilities to ensure that the fuel assemblies are installed onto the fuel supports in the orientation within the core as designed and specified. Orientation of the fuel assemblies are the responsibility of the fuel assembly installation personnel based on a visual inspection. As such, a typical problem encountered with reactor design implementation is errors due to fuel assemblies being installed having an incorrect orientation which is commonly referred to as rotated bundle error. As identified by the inventors hereof, an improved assembly and method for eliminating or at least minimizing rotated bundle error would be desirable.